Translation memory functions disabled

While working on a project this week, I suddenly noticed that I could not "fetch" a translation from the "Translation Results" window, using the Ctrl-T shortcut. Neither could I move around in Translation Results with Alt+PageDown (PageUp).

I actually noticed that all the Translation Memory functions in the ribbon had been greyed out and disabled.

Like this:

This seems to be similar to what is experienced by some after the update of the service pack, but for me it happened just before, and has persisted after I installed the service pack.

I have checked the shortcuts and they are the same. No settings seem to have been changed. I even tried "Reset Windows Layout", but to no avail.

This is a pretty serious functionality fault, which I would very much like to have corrected ASAP.